The invention relates to a spindle drive comprising a threaded spindle that can be driven rotationally, a carriage displaceable along a guide rail via said threaded spindle, as well as several guide carriages arranged in front and behind the carriage in the direction of the spindle axis for supporting the threaded spindle, with in an advancing motion of the carriage the guide carriages arranged in front thereof being successively pushed together by the carriage and moved towards one end of the spindle, and with the guide carriages arranged behind the carriage being dragged via a coupling mechanism and being moved into an allocated support position.
Such spindle drives are frequently used for a motorized drive of linearly movable parts, for example machine tables, coordinate measurement devices, and the like. In the part to be moved a spindle nut is arranged with an internal thread matching the external thread of the threaded spindle, which during the rotation of the threaded spindle, is moved along the spindle axis and entrains the part to be moved.
In such a spindle drive the maximum drive speed of the carriage depends on the critical rotation speed of the threaded spindle. Upon reaching the critical rotation the threaded spindle is set into natural oscillation, which aggravates a precise positioning of the carriage or renders it even impossible. Relevant factors determining a critical rotation speed are the diameter of the threaded spindle and particularly its length. The smaller the ratio of the diameter in reference to the length of the threaded spindle the lower the critical rotation speed of the threaded spindle and thus the feed rate that can be achieved. Due to the fact that particularly in large length threaded spindles (e.g., several meters) the diameter of the spindle cannot be arbitrarily increased for reasons of dimensions and/or weight, such threaded spindles are additionally supported by so-called guide carriages in the area between the carriage and the end of the spindle, so that the length of the free, not supported spindle sections is shortened. The critical rotation speed of the threaded spindles and thus the maximum feed rate of the carriage achievable can be considerably increased this way. In a feed motion, the guide carriages are pushed together in a shortening spindle section and moved towards the allocated end of the spindle, while the guide carriages are distributed over the extending spindle section in a continuously adjusted fashion.
From DE 196 36 272 A1 a spindle drive is known in which the guide carriages, here called spindle support units, are connected to each other in pairs or via a pulley-like connection to the carriage. As is easily discernible, for example from FIG. 10 of this publication, such solutions are of extremely complicated construction and extensive in their technical assembly because numerous pulley cables must be installed and connected to the guide carriage and/or the carriage. This particularly applies if more than two guide carriages are arranged in front and/or behind the carriage so that such a design with more than two guide carriages can hardly be implemented according to this principle.